1. Field of the Invention
The present invention relates to an image read-out device for use in a digital copying machine or an image scanner.
2. Description of Related Art
In an image read-out device, in which light is emitted from a light source toward an image surface, and the light reflected by the image surface is reflected by a mirror, and then reflected light is read out by an image sensor through an image forming lens, an image read-out device employing an integral type scanning optical system unit integrally storing these components together is well known.
Recently, the image read-out devices are often incorporated into copying machines such as digital compound machines.
The image read-out device may also be provided on a portable image scanner.
If the image read-out device is incorporated into a digital compound machine, it is preferable for it to be miniaturized. If the image read-out device is incorporated into an image scanner, since it is required to be lighter and compact, it is further preferable that it be miniaturized. Furthermore, it is desired that the image be clearer.
In order to respond to such needs, for example, JP-2001-174932-A1 proposes an image read-out device in which a read-out magnification is enhanced, and a width along a sub scanning direction is reduced by obtaining a short conjugated length employing a multi-reflective mirror which reflects luminous flux from a document several times.
Further, JP-2000-50031-A1 discloses an apparatus that positions a mirror optically nearest to a document surface side among a plurality of mirrors, between the optical axis and the document surface and located between an incident surface of the image forming lens and the read-out device, thereby obtaining a shorter conjugate length, enhancing the read-out magnification, and enabling miniaturization.
However, in any device, heat evolved by a light source or an image sensor is not considered, and thus the degradation of read-out accuracy occurring due to the thermal expansion of a member has not been alleviated.
As a read-out device in consideration of the thermal expansion of a member, for example, JP-2004-126447-A1 proposes an apparatus in which, by positioning a reflective mirror before or after an image forming lens and thus folding luminous flux back in a vertical upwards direction of a scanning unit, an image sensor such as CCD and the like is positioned above the image forming mirror in order not to give the heat evolved from the image sensor to the other optical elements.
However, positioning the image sensor above the integrally formed scanning optical system unit it leads to spoiling the appearance, and a user operating the apparatus happens to see the electrical wiring, which spoils the appearance of the apparatus.
Further, since the light source and the image sensor are contained within a carriage, the temperature in the carriage sequentially rises and, finally, thermally expands the other optical components in the carriage, thereby, the degradation of read-out accuracy cannot be avoided.